On the endurance cars like our GrandAm GT or ALMS GT2 car if we could see on track oil temps of 230-250 degree's that car will go 24 hrs on track no problem at all. Limited time above 270-290 is ok, given the car still has good oil pressure but the oils most certainly start to break down at that point. Of course I am talking about quality synthetic oils, not the standard dino stuff.